Stepping motor exciter apparatus and method

ABSTRACT

Disclosed is a salient pole stepping motor combined with high frequency current regulating chopper mode excitation apparatus connected to differentially excite at least two sets of electrical windings of the stepping motor in an excitation method wherein winding current is responsive to instantaneous rotor produced changes in electrical winding inductance.

United-States Paten [191 Bruckner et a1;

11] 3,750,000 1 July 31, 1973 STEPPING MOTOR EXCITER APPARATUS ANDMETHOD [75] Inventors: Ronald L. Bruckner,Iaiiie s E; Helmbold, both ofDayton, Ohio [73] Assignee: The National Cash Register Company, Dayton,Ohio [22] Filed: June 19, 1972 [21] Appl. No.: 264,173

' 51 Int. Cl. H02k 37/00 [58] Field of Search 318/685, 696, 138,318/254, 341, 439, 432, 434

[ I Reierences Cited UNITED STATES PATENTS 3,452,263 6/1969 Newell318/696 lOl I021 I04 I08 Q 7 CLOCK I09 3,345,547 I 10/1967 Dunne 318/6963,466,520 9/1969 Aylikei et a1. 318/696 Primary Examiner-G. R. SimmonsAttorney-J. T. Cavender, Wilbert Hawk, Jr. et al.,

[57] ABSTRACT Disclosed is-a salient pole stepping motor combined withhigh frequency current regulating chopper mode excitation apparatusconnected to differentially excite at least two sets of electricalwindings of the stepping motor in an excitation method wherein windingcurrent is responsive to instantaneous rotor produced changes inelectrical winding inductance.

19 Claims, 6 Drawing Figures PATENTEDJULSI I973 sum 1 0r 3 FIG. 6

TIME

Pmmmw I 3.750.000

SHEEI 3 BF 3 FIG. 4

EXClTER- APPARATUS AND METHOD .fl h qii s for qr h vicesi 2. Descriptionof; the Prior Art I Excitation of asteppingmotor with a switchmodu ,lated or Chopped sourceof-direct current energy is described in; the paperDrive=System for Small or Large Angle PM Stepping. Motors by Thomas E.Beling, which was publishedin the Mar. 17, 1971 issue of the magazineComputer Design at pages. 77 to 82. 'Althoughsuch paper by MrgBelingdescribes the concept of stepping motor. chopper excitation, it does notdisclose the concept of I differentially exciting several windings ofvastepping motor from a chopper source or the improved motor performancesresulting therefrom. Mr. Belings paper also does notdisclose the.concept of externally controlling the operating frequency of thechopperapparatus nor does itmention the use of chopping regulators orreluctance stepping motor.

1 US. Pat. No. 3,355,646, issued Nov. 28 1967 on the application of Mr.Tatsuo Goto of Hachioji-shi, Japan disclosesthe concept-of. exciting asteppingmotor with B EF nsscm ouop DRAw FIG. 1 .of the drawings isanelectrical schematic diagram of a stepping motor s ystem made accordingto'the with the rotor and =stator members located a'pole pulses of.energy. In- Mr. Gotos patent, the energy pulsesare'obtained fromanalternating current supply and fromabi-level direct current source, Mr.Gotos inventiondoes not differentially excite windings of the stepping,motor nor does it employ high frequency chopping apparatus. y i g v TheProduct Data Sheet number I-I-770 published by Sigmav Instruments 1Incorporated of .Braintree, Massachusetts 02 185, United States vofAmerica, also, describes a. chopper excitation systemv for a steppingmotor device..The Sigma chopper system also does not employdifferentialwinding excitation or external control of the choppingfrequency. 4 I

,Bi-phase excitation of a stepping motor wherein the stepping positiondetents are located generally halfway between stator poles is also'known inthe prior art. US. Pat No. 2,596,71 l, issued May I 3, .1952 onthe application of .R. l (..Mueller, and ,U.S. Pat. No. 3,374,410,issued Mar. 19, l968-onthe application of D. H. Cronquis t et al., bothdescribe the conceptof simultaneously exciting at least two sets ofmotor stator windingsin order that a rotor detent position be createdgenerally halfway between stator poles. i

BRIEF S'UMMARYOF INVENTION v I-Excitationof a stepping motor fromachopper modu-. lated source is combinedwith bi-phase operation of themotor wherein at least'two windings are differentially energizedanddefine stepping detents located. generally halfway intermediate twosuccessive pole aligned conditions. In the differentiallyexcitedwindings, the chopper modulated excitation current having analternating current component is dividedv inversely according towindinginductance and the motors instantaneous rotor-stator polealignment and is dynamically responsive aligned stepping detentposition. FIG.'3 of the drawings schematically shows 'the internal partsof a bi-ph'ase excited'steppingmotor'with the rotor and stator memberslocated just pastan intermediatedetent position. I V FIG; 4 of thedrawings schematicallyshows the internal parts of the bi-phase excitedstepping motor of FIG. 3 with the rotor and stator members located justpast an intermediate detent position; 1 r f i FIG. 5 of thedrawingsschematically's'hows th internal parts of a bi-phase excitedsteppingmotorhavinga modified interconnection of stator windings; "FIG-6 of thedrawings shows'a waveformtypicalof the current flowing-in windings oftheFIGS." -3 and" motor. I t 'I I DETAILEDGD ES CRIPTION"OF INVENTIQNQQEfiective utilization of a'stepping'motoris' known to requireconsideration of the"electricalcircuitryei'n ployed to excitethesteppingmo'tor windings: It-is common practicefor-instance toemploy-constanfvolta'g'e excitation of stepping :motor windings whenthemotor is used in a relatively slowspeed environment and-the electricaltime constant delay inherent in suchexcita tion cansbetolerated. Itis'also common practice-to em:

ploy constant current excitation of the-motor windin gs inapplicationsdemanding increased operating speed from I the motor. In many instances,however, the high power dissipation and the poor motor dampingcharacteristics associated with constant current excitation detract from theadvantages of increasedstepping-speed so that'some other mode ofoperation is desirableRecently the use of achopper o'rswitchingmodecurrent regulator. for 'motor' excitation" has"becomepopular since the stepping 'motor driven by such apparatus operates with improved speed, power dissipation and damping when comparedwith either of the classical citing techniques. The switching modecurrent regulator circuit'provides'a desirable high "overall power emciency and when employed-with thebi-phasefexcitation;

method, wherein 'at least-two motor windings are ex cited and a rotorstepping position" or dete'nt is thereby located generally midwaybetween two pole aligned conditions,'provides unusually good 'rotorda'rnpin'g characteristics. 1

FIG. lof'the-drawings shows in schematicdiagr am" form a switching modecurrent regulator which is suitable for stepping motorexcitation. The"FIG'. 1 circuit is suitable for use with either a bi-phase orfaconvert-1' tional'single winding method.however,it provides sig'gnificant performance advantages when used in' abif phase excitationarrangement.-

ELECTRONIC ciaculfr if The FIG. 1 circuit consists of a switchingdevicesuch" as operational amplifier connected toja" group'off switchingtransistors 118, 124 and 126with the driven" motor windings l40and l42being connected into the emitter current path of the final switching"transistor 126. The operational amplifier 1 10, the transistors 1 18,124, 126 and the motor windings 140 and 142 are all part of a feedbackloop identified by the arrow 182. The FIG. 1 circuitalso includes theinput signal path components at 101 and 177 which lie outside thefeedback loop so identified by the arrow 182.

The-transistor 126 in FIG. 1 is placed in a conducting state by signalsreceived from terminal 102 through node 109 and the operationalamplifier 110. Conduction in the transistor 126 occurs in the saturatedmode with the primary path for the conducted current being between thevoltage source V at terminal 130 through transistor 126, node 184 andthe parallel-connected motor windings 140 and 142, through the node 150and through the current sensing resistance 148 into the ground terminal149 and thence the source V Once conduction in the transistor 126 isinitiated, it continues until the signal developed across the currentsensing resistance 148 becomes more positive than the voltage at circuitnode 109. During a-steady state operation of the FIG. 1 circuitry, aclock signal similar to the waveform shown at 100 is applied at terminal102 and is transmitted through the A.C. coupling network includingcapacitor 104 and diodes 106 and 108 and through node 109 into thepositive terminal of operational amplifier 110. Thisclock' signalinitiates the conduction period which is terminated by signals devel-'oped across the current sensing resistance 148, the circuitry being inthe fully-on stage during a conduction period and in the fully-off stageduring the nonconduction period. Regulation of the current flow in motorwindings 140 and 142 occurs by way of the signals traveling around thefeed-back loop identified by arrow 182. This signal determines theduration of current conduction in transistor 126 once such currentconduction is initiated by the clock pulses applied at terminal 102. v

The operational amplifier 110 in FIG. 1 is connected to operate in theswitching rather than the linear mode of-operation, that is, theamplifier is used in the manner of a Schmitt trigger circuit rather thana linear amplifier circuit. In this mode of operation, the amplifiersoutput signal will correlate with the larger of its positive andnegative input signals and will be at either the positive or negativeoutput limit of the amplifier.

The circuit elements at 177 in FIG. 1 provide a selectable level biassignal to the positive input terminal of operational amplifier 110. Onelevel of this selectable level signal causes the FIG. 1 circuit togenerate normal motor current while the other provides a reducedmagnitude current to the motor windings for use in generating thereduced amount of torque needed in holding (as opposed to moving oraccelerating) the rotor of the motor in a stationary position. Reducedholding current provides lower power dissipation and reduced motorheating during long periods of maintaining the motor rotor in a lockedstationary condition. The bias circuit shown at 177 in FIG. 1 consistsof switching transistor 170 which controls the voltage developed at theslider of potentiometer 162 by way of altering the division ratio of thevoltage divider consisting of resistors 166 and 164 and thepotentiometer 162. When the switching transistor 170 is in thenonconducting state, current from the resistor 168 flows through diode180 and provides a higher voltage atthe slider of potentiometer 162 thanis the condition when transistor 170 is in the conducting state. Thesignal which determines the conducting and nonconducting times of thetransistor 170 is identified as a hold signal and is applied as apositive-going pulse at terminal 178 for transmission through theresistors 176 and 174 to the switching transistor'170. The voltagedeveloped at the slider of potentiometer 162 is derived from a regulatedsource V applied at terminal 172, and is filtered by the capacitor 160and applied through the resistor 158 to the node 109 and the-operationalamplifier 110. When the higher level signal from the bias circuit 177 isapplied through the resistor 158 to the operational amplifier 110, thecurrent in motor windings 140 and 142 flows for a longer time followingeach clock turnon and hence produces the normal higher average currentflow in the motor windings 140 and 142. The holding current level can beselected as any desired fraction of the normal current one-third andone-half having been employed in the preferred embodiment by anappropriate selection of values for resistors 162, 164, 166 and 168.

Several of the components shown in FIG. 1 are incorporated in thecircuit to provide the environment necessary for functioning of theactive components in the circuit, this being true of the resistor 154and the capacitor 156 which remove high frequency components from thefeed-back signal. The diode-resistor network 1 12 and thecapacitor-resistor network 1 14 provide DC and AC hysteresischaracteristics for the operational amplifier 110. The resistors 116,120 and 122 provide the necessary bias and switching currents for thetransistors 118, 124 and 126 in the manner which is known.

in the art. The capacitor 128 provides filtering and noise suppressionfor the source V, at terminal 130.

The diode 132 and the resistor 134 provide the con ventionalfree-wheeling current path for currents generated by the energy storedin motor windings 140 and 142 during the time transistor 126 is in theoff condition. In practice, it has been found desirable to use a fastrecovery diode having a recovery time near 0.3 microseconds from the 2ampere conduction state (or a Schottky Barrier diode) in the position ofdiode 132 in the FIG. 1 circuitry.

As a result of the rapid and large current changes in the conductor 127,the diode 132, and the windings 140 and 142, signals from these parts ofthe circuit have been found capable of radiating into low level portionsof the circuit. Through the use of an RC circuit including capacitor 136and resistor 138, the fall time of the current in conductor 127 islimited to slower values providing less interference in the low levelcircuitry.

In practicing the invention, it has been found possible to fabricate allof the FIG. 1 circuitry except the power transistor 126, the motorwindings 140 and 142 and the current sensing resistance 148 into ahybrid circuit module containing a mixture of integrated and discretecomponents and with only the terminals 125, 130, 152, and 178 beingbrought out of the hybrid package for external connection. Additionalhigh current switching elements may also be inserted into the FIG. 1circuit in series with each of the motor windings 140 and 142 and inlieu of the jumpers at 144 and 146 in order that the regulated outputcurrent from the FIG. 1 apparatus be commutated between windings of thestepping motor.

Where the stepping motor coupled to the FIG. 1 circuit includes two ormore windings requiring simultaneous in-phase excitation, as is, forexample, the case for the two windings 340 and 342 located at similarpositions on diametrically opposite sides of the FIG. 3 motor, the groupof similarly phased windings may be connected in series or paralleltoform a composite winding as shown at L 140 and L 142 in FIG. 1.

Many of the switching mode or chopper current regulator circuits knownin the prior art operate in the free-running mode wherein both theinitiation and the termination of a current pulse are dependent uponelectrical time constants found in the motor winding inductance or thepower supply. The regulator circuit of FIG. 1 is capable of operating inthis free-running or self-timed mode simply by omitting the clock signalfrom terminal 102. Clock triggering or initiation of the current flowperiods in the FIG. 1 circuit has been found to be desirable since itassures stable operation of the regulator circuit in the pulse-widthmodulating mode. The use of an ultrasonic frequency clock signal such asthat shown at 100 in FIG. 1 assures that this stable operating modeproduces pulses of current and fier 110 has this lower output voltage.If the diode 113 ent switching point exists for the operationalamplifier l 10 than when the diode 113 is conducting. In a similarmanner the RC network 1 14 provides an AC hysteresis or separationbetween the ON and OFF points of the magnetic flux at a rate above theaudio frequency range. These pulses are less likely to produce humanaudible noise from the stepping motor excited by the FIG. 1 apparatus.

The clock signal shown in FIG. l consists of a 4 microsecond pulse whichoccurs every 50 microseconds. This 4 microsecond pulse initiates aconduction period in the operational amplifier 110 and the transistor126 every- 50 microseconds or at a 20 kilohertz rate. The duration ofthis conduction period may be short or long depending upon the currentregulating action of the feed-back loop designated by arrow 182. Sincethe circuitry of FIG. 1 may be used with a stepping motor employed in abusiness machine environment, motor excitation at a frequency which isabove the human audible range during all possible regulator conditionshas been found desirable in order that objectionable noise from thestepping motor laminations be avoided.

In FIG. 6 of the drawings, there is shown an idealized waveform which isdescriptive of the chopper regulated current flowing in the'currentsensing resistance 148 during a typical current build-up and steadystate operation of the FIG. 1 circuit.

In the FIG. 6 drawing the transistor 126 begins conduction at the point610. Following this initiation of conduction, current in the motorwindings and the sensing resistance 148 increases according to the curve602 and at a rate determined by the inductance'of the motor windings andthe resistance of the motor windings and the other components in thecurrent path. As shown at 608, this portion of the FIG. 6 curve isidentified as having characteristics defined by the fractionInductance/Resistance or L/R. At the point 612 in FIG. 6, the currenthasreached a magnitude satisfying the signal existing at node 109 of theFIG. 1 circuit and the power transistor 126 is placed in the off stateby signal from the operationalamplifier 110. Following turn off of thepower transistor 126, the winding current decays along-the curve 614until a clock pulse initiates another ON period in the operationalamplifier 110.

The diode and resistance network 112 surrounding the operationalamplifier l 10 allows a DC hysteresis or a separation between the on andoff points of the operational amplifier by altering the normal potentialat node 109 when the amplifier 110 has an output at the lower of its twooutput levels. The diode 113 is in the conducting forward biasedcondition when the amplioperational amplifier 110 by altering thepotential at node 109 according to the recent changes in state of theamplifier output terminaL'The AC hysteresis characteristic is useful inproviding noise immunity for the operational amplifier 110.

Normally the operational amplifier 110 is placed in conduction at thepoint 604 (FIG. 6) by re-appearance of a clock pulse at terminal 102 inFIG. 1, however, if the clock pulse is omitted and the current in motorwindings 140, 142 and the sensing resistance 148 decays to asufficiently low value that the signal at node 109 including hysteresisis more positive than the signal at the negative input terminal of theoperational amplifier 110, the operational amplifier will be turned oneven though the clock pulse is absent and transistor 126 will again beplaced in the conducting state.

As shown at 606 in FIG. 6, the initiation of current flow in the motorwindings 140 and 142 occurs at a ZOKI-I rate whenthe system is driven bythe clock waveform shown at in FIG. 1. The current curve in FIG. 6 isshown interrupted at the point 616 in order that both the overallcurrent waveshape and the chopping ripple on the current waveform duringregulation is viewable. In the preferred embodiment of the invention,the chopping ripple during steady state operation has been found to benear 10 percent of the regulated current amplitude indicated at 600 inFIG. 6.

During the portions of FIG. 6 which are similar to the part indicated at614, that is, the time when the transistor 126 is in the open state,current flows in the free wheeling network composed of diode 132 andresistor 134 in FIG. 1. Also, as shown in the part of FIG. 6 between thepoints 610 and 612, the switching regulator of the invention does notcommence regulating action until current in the windings builds up tosome minimum value, that is, until the inductive delay in the motorwindings is overcome. 1

In a manner similar to the 610-612 portion of the FIG. 6 curve, theregulator circuit may also lose control of the motor current when, forexample, in a business machine environment, the motor is operated in theslewing mode wherein rapid rotation past a number of stepping detentpositions occurs and large values of EMF are induced in the motorwindings. Low winding inductance and high supply voltage at tenninal mayalso be used to reduce the non-regulating time of the FIG. 1 circuitryduring motor slewing. Since use of the stepping motor with relativelylow winding inductance is already necessary in the invention in orderthat sufi'icient exciting current be developed from the ZOKI-Iichoppersource, the use of low inductance and high supply voltage to permitregulator action during slewing is not a severe limitation.

STEPPING MOTOR vices in FIGS. 2-5 each includes an eight pole stator anda six pole rotor. In FIG. 2 these stator and rotor elements areidentified with the numbers 202 and200, respectively, in FIG. 3 with thenumbers 302 and 300, respectively, and in FIG. 5 with the numbers 502and 500, respectively. Since the motor shown in FIG. 4 is the same motoras that shown in FIG. 3, the component designations used in FIG. 3 arecarried into FIG. 4. The

be engaged in a conventional detent position wherein rotor pole 248 ismagnetically engaged with stator pole 208 and the opposite rotor pole252 is engaged with stator. pole 216, and wherein none of the otherrotor or stator poles are fully engaged. The magnetic flux for engagingthe rotor and stator poles in the position shown in FIG. 2 can begenerated by windings such as winding 206 and winding 224 locatedrespectively on the stator poles 208 and 216. It is also possible togenerate this magnetic flux with windings located toroidally around themotor stator as shown at 27lin FIG.

In FIG. 3 of the drawings, the stepping motor is illustrated with therotor in an intermediate detent position which is located generallyhalfway between two successive conventional detent positions of the typeillustrated in FIG. 2. As illustrated, the rotor 300 is in anintermediate detent position wherein both the adjacent rotor poles348and 350 are partially engaged with the respective stator poles 308 and310. The intermediate detent position engagement of rotor 300 in FIG. 3is the result of bi-phase excitation of windings 306 and 342 and thesimilar but oppositely placed windings 324 and 340 on the stepping motorstator 302. In this bi-phase winding excitation, it is assumed thatwindings located on similar but oppositely placed poles, such as poles310 and 318, are connected together electrically in a series or parallelarrangement according to convenience. It is important however in thepresent invention that the windings 306 and 342 be parallel excited inthe I manner shown for motor windings L1 and L2 in FIG.-

' In the bi-phase rotor detent position shown in FIG. 3, the tendency ofa movable magnetic circuit apparatus to minimizethe total air gapencountered by its exciting magnetic flux is determinative of the detentposition. This tendency to minimize the air gap, in the eight polestator and six pole rotor configuration, dictates that the rotor assumethe intermediate detent position-of FIG. 3, wherein partial andapproximately equal engagements occur between rotor pole 348 and statorpole. 308 and rotor pole 350 and stator pole 310 with the amount ofnon-engaged rotor 344 on pole 348 being approximately equal to theamount of non-engaged rotor 346 on pole 350 and with similar conditionsprevailing for the opposite rotor poles 354 and 352 at the bottom ofFIG. 3.

When the bi-phase excitation method is combined with a switching currentregulator or chopper regulator of the type shown in FIG. 1, it is foundthat the kinetic energy dissipative damping which tends to dissipaterotational movement energy from the rotor exceeds the amount of dampingfound in a motor excited with constant current. I

In FIG. 4 the stepping motor in FIG. 3 is shown with the rotor 300located in the position it could assume during an overshoot movement. InFIG. 4, the rotor 300 is presumed to have been moving in a clockwisedirection with the intended detent or stop-position being the positionshown in FIG. 3; however, the inertia of rotor 300 and its connectedload are presumed to have carried the rotor 300 beyond the intendeddetent position shown in FIG. 3.

When the rotor 300 is located in the position shown in FIG. 4, it isfound that the electrical inductance of winding 306 associated withstator pole 308 exceeds by a significant amount the electricalinductance of winding 342 associated with stator pole 310. Thedifference in electrical inductance between winding 306 and winding 342is a result of the relatively good engagement between stator pole 308and rotor pole 348 and the relatively poor engagement between statorpole 310 and rotor pole 350.

Since the windings 306 and 342 are connected in parallel and excited bythe same voltage inthe manner shown for windings L1, 140, and L2, 142 inFIG. 1, and since the current produced by the switching regulatorcircuit of FIG. 1 has an alternating current component, it follows thatthe different electrical inductance of winding 306 and winding 342 inthe FIG. 4 rotor'position will result in different current flows in thewindings 306 and 342 the currents being inversely proportional to theinstantaneous inductance of the windings 306 and 342. In the FIG. 4position of rotor 300, the large inductance of winding 306 produces alesser current flow in this winding than the current flow in winding 342which has a small inductance and a larger current flow. Since thewindings 306 and 342 are excited in a differential manner by aregulating current source, the total current shared by the two windings306 and 342 is constant and the current flowing in each of theconfiguration of FIG. 4 produces an especially large difference incurrents between the windings 306 and 342; a ratio of 3 to 1 between thewinding currents being encountered in ordinary use of the invention.

An important benefit results from the large current flow in winding 342and the smaller current flow in winding 306. This difference in currentscorrelates precisely with that which is needed to return the rotor 300from the overshoot position of FIG. 4 to the desired detent position ofFIG. 3. Hence, the combination of a chopper power source anddifferential excitation of the two windings 306 and 342 in a bi-phaseexciting arrangement results in the rotor 300 automatically influencingthe motor winding current as it rotates with the influence being suchthat the altered currents tend to oppose rotor position overshooting.Rotor position responsive stator currents would not be possible in thepresent invention if the windings were not:

I. excited with current having an A.C. component;

2. excited in a differential manner with a total current of determinedmagnitude; and

ISTEPPING MOTOR MAGNETIC FLU-X f I is also affected by the-methodof-"winding interconnem tion selected for the motor.

In the conventional .detent stepping motor shown in FIG. 2 of thedrawings, amajorportionofthemagnetic flux generated in stator 'pole 208-flows along the paths 232 and 226 into the rotor and stator polesadjacentthe engaged rotor and stator :pole pair. Even though a a majorportion of the flux from stator pole' 208follows '2 flow-acrosstherotorlikeis done in the FIG. 3 r'notor such paths 226 and 232,-asignifi'cant portion ofthis I .flux also follows therminoripaths 228an'd'230-which involve .the partially .engaged'stator' poles 2 l 4 and-218. The fluxpattern illustrated for thestator'pole' 208 is reunder theconditions of b'i-ph jase" winding excitation w ith av switching modecurrent regulator 'asdisclosed in "thisspecific'ation. Part of themagnetic flux' patli sre- 5 sulting'from' the magnetic "poleconfigutation'shown in 5 ,Several methods.foriinterconnecting windingson the stator poles 308, 310,312, 314, 3 16, 3'18, 320 and322 inFIG.3.areknown'inzthe art. Thepath traveledby the motor magnetic flux-variesaccording "to the particular FIGL'S are illustrated'by thepaths'at 5 60, 568, and 562. An exact desoription of'the' fflow in flux paths cr meF [GE 5 "motoiifws w l as the FIG.

3 motor) has been found defin- 10 able'onlywiththe*"a'id"fof"differential equations and "computer aided solution ofthese, equations.

I One" important "is found between motorsexcited according'to the FIG. 5pole arrangement as compared with the FIG. 3 pole arrangement, 'in" thatduring all except one of thesteppingmovements ofthe rotor 500 in FIG. 5,motor magnetic flux t'ravels from one stator pole across the f rotorstr't'icture into one I or moreother stator poles. During this onestepping "movement "of the rotor 500, however, flux does not f' bubdnstead flows"between' two 'adjacent stator'lp'oles 514 and 516 whiehhave'oppo'sit'e' magnetic polarity. It

is'found in practice that a significantdifference in rotor torque and"alsoa significant difference in the rotor peated for the stator'pole216 locate'd atthe bottom of 'zi damping characteristicsare'observedbetween the adja- FIG. 2 andis partially illustrated by th'e "arrows-234 which are. shown diverging in the -rotor 200. I

The flux pattern described above" for -therelatively simple'FIG, 2 caseof rotor and stator polesdirectly en- 3 of the drawings. In FIG.3, whereboth the windings 306 and 342 are excited, part of the magnetic fluxfrom stator pole 308 travels in the adjacent stator pole310 I whileanother part follows the path 3'32 through the slightly engagedstator'pole 322. Still an additional part flows according to the path328 through the partially engaged stator pole-3l4anda sm'alleramounttravels through each ofthe rotor and stator poles'of the motor. It issignificant in FIG. 3 that all of theffluxoriginating in statorlpole 308is notrequired toireturn' through stator pole 310-but that sizable'portionsof this flux can travel across the structureof rotor300 andreturn'to the stator through other rotor andj'stator'pole'pairs. If itwere necessary that all of thefluxjorigi'nating in stator pole 308return from. the rotor 300'via statorpole 310, it wouldbe impossible forthe windings306-an'd '342'to have significantly-differentvaluesofelectrical inductance since the sameflux would, flow in. both poles-308and 310 and would engage bothwindings306 and 342. The significantlydifferent "values of electrical inductanceare needed to obtain thedesired differentialdivision of winding currentsasdescribed'forwindings306 I and 342. t

The flux paths'illustrated in FIG/3 are established in the eight polestator, six pole rotormotor under the condition of alternatingmagnetic-polarityinthe' stator ce'nt pole and the across-the-rotor fluxpaths for the FIG. 5 motor.

To move therotor 300 in FIG. 4-into the stepping detentposition shown,it was necessary that windings 342 .g g on a one-H3116 basis is fi q rly j' -and 306"be energized. To move the rotor 300 into the for thebi-phase excitation arrangement' shown in FIG.

"next upcoming "stepping detent positionin the' cloc'k- "wise directionindicated" by the arrow 313, it is neoes- 1 sary that. the winding 343and the winding 306 be'concurrently energized." For the eight polestator, six pole 'rotor motor shown 'in FIGSf2-5, a pole energi'zationsequence which moves opposite the direction of rotor 1 rotation isrequired. "The 'commutationfrom current flowing in winding342-to-current flowing in winding 343 in FIG.'4 is accomplished byswitching transistors located at the position of jumpers 144 and 146 inFIG. 1. In a practical embodiment of the FIG. 1 system using one of themotors shown inFIGS'f2-5, there areactually four winding setsrather thansimply the two windings and 142' connected to' the "circuit node 184,one of which ""four sets isfor each of the=four diametrically opposedpairs of stator pole'sfSince the two windings 140 and -142aredescriptive of the inventive concept of the FIG. 1 system, the practicalembodiment-of the four windings are thus omitted; Similarly omitted fromthe FIG. 1 system is the free wheeling diode network which provides'apath" for the stored energy current from windings 1'40 and 142 when.jcommutating switches at jumper positions 144' and 146 are opened.These free wheeling diode networks are connected as shown by the dottedlines associatedwith diode 131 and resistor abruptly interrupted levelofwinding 342, there exists I a period during commutation wherein theconstant current regulating action o fthe FIG. "1' apparatus causes A 11current in the non' comm utated winding 306 to beincreased in magnitude.This increased current magnitude in such winding 306 is beneficial tostepping motor performance since it provides increased magnetic flux andincreased pole strength in stator pole 308 and thereby increases theforce attracting rotor 300 to the next stepping detent position. 7

Depending uponithe supply voltage and the electrical time constants ofthe commutated windings 342 and 343 in FIG. 4, it isof course possiblefor the chopping regulator apparatus of FIG. I to cease regulating andbecome saturated during commutation since the abrupt interruption ofcurrent inthe turned-off winding 342 occurs more rapidly than currentcan increase in the newly turned on winding 343 or the noncommutatedwinding 3 06. 1

, The current flowing from the switching chopping regulator to thestepping motor windings is described herein as having an alternatingcurrent component or being undulating in nature. In so describing thewinding v current, it is recognized that the current resulting fromopening and closing switching transistor 126 in FIG. 1 would, in thecase of a resistive load, appear as a series of unidirectional or DCcurrent pulses andthat the inductance of windings 140 and 142 tends tosmooth these pulses of current into a constant flow. Despite thissmoothing, current having an alternating current component aptlydescribes the regulated current waveform since at least some pulsing orundulations of current remain after the smoothing and since a Fourier'series analysis of the winding current would show it to include atleast a DC component and one AC component.

The tendency of chopper derived differential currents flowing inwindings 306 and'342 (FIGS. 3 and 4) to urge an overshooting or anoscillatingmotor rotor into its intended stepping detent positionisespecially significant when the performance of a motor excited with theFIG. 1 systemis compared with that of a motor having a constant currentflowing in each excited winding. If the rotor of the constant currentexcited motor overshoots an intended detent position (ofthe bi-phasetype shown in FIG. 4), the rotor-stator pole pair having the bestalignment condition (poles 308 and 348 in FIG. 4) 'will tend to attractthe rotor to the overshoot position or hold it in this position onceattained. Since this best aligned pole pair is energized with fullexciting current in the constant current case and the aligned polesprovide a good flux path, this attracting or holding in the overshootposition is especially strong. Moreover once the rotor attains theovershoot position the rotor-stator pole pair which should be mosteffective in returning the rotor to the intended detent. position (poles310 and 350 in FIG. 4) will be handicapped by poor engagement and theresulting smaller magnetic flux and magnetic force even though such pairis excited by full winding current.

In the laboratory a motor excited with constant current in each of thebi-phase excited windings has been observed to oscillate around theintended detent position for a prolonged period as a result of thisstrong force in the overshoot aligned poles and weak force in theovershoot correcting poles. When the same motor is energized with theFIG. 1 system in lieu of a constant current apparatus, a significantdifference occurs. in both the overshoot aligned pole pair and thepolepair which should be most effective in returning the rotor to willalso cause the pole pairwhich should be most effective in returning therotor to the detent position (poles 310 and 350 in FIG. 4) to be excitedby a greater than normal current and hence to be more effective thannormal in correcting the overshoot condition."

Once the rotor attains the intended detent position after the overshootis corrected, current in the two biphase windings 140 and 142 ofthe FIG.l system will of course equalize because of the equalinductance in thewindings. 1

In addition to. the'magnetic flux magnitudes which are responsive topositioning of the stepping motor rotor, ,thepresentinvention is alsobelieved to provide increased kinetic. energy dissipatingabilityor-damping over the stepping motor apparatus of the prior art. Thisenergy dissipating capability or damping is believed 'to involvethelargechanges of rotor and stator magnetic flux which occur as therotor moves about the intended detent position. These large magneticflux changes are believed to dissipate kinetic energy through themechanisms of. magnetic hysteresis and eddy currents in the motorstructure in the manner known in the art and possibly to involvedissipation in some of the electrical components conducting. currentduring the oscillating period. w

In the present invention, a particular form of stepping .motor excitingcurrent together with: a particular arrangement of motor -windingsallows the motor winding current to be automatically responsive to theposition I of the stepping motor rotor and causes the motor rotor to bepositively retained ina stepping detent position. Operation of theinventionhas been described in terms of winding inductance flux flow inthe stepping motor. Itis also known that voltages are induced in thestepping motor windings as the alignment of rotor and stator polesischangedThe effect of these induced voltages on the currents in themotor windings has been described herein only'in "connection with aslewing mode of operation of the motor since changes in'windinginductance and magnetic flux are believed most significant in such typeoperationof the apparatus.

While the system and apparatus hereof accomplishes the objects andadvantages mentioned, certain variations may occur to those skilled inthe art and itis contemplated that all such variations not departingfrom the'spirit and scope of the invention hereof are to be construed inaccordance with the following claims. What is claimed is: I l 1.Electrical transducerapparatus-comprising: an electrical stepping'motorof the type having a rotor member which is magnetically positionable ina plurality of detent positions each located generally intermediate twoadjacent pole aligned detent positions by simultaneous excitationof twoelectri cal windings, each winding beingassociated with one pole of saidadjacent pole-aligned detent posiferentially with said two electricalwindings for supcommutating means connected with each electrical windingof said stepping motor and with said electrical exciting meansfordiverting said differentially divided exciting current to subsequentpairs of electrical windings; I I r whereby the electrical inductance ofeach winding of said, two differentially connected windingsis dependentuponthe degree of alignment between rotor and stator polesinstantaneously associated with said winding and current divisionbetween said differentially connected windings is responsive to saidelectrical inductanceand to said" degree of alignment for producinghighcurrent flow in a winding associated with a poorly alignedrotorstator pole pair and low current flow in a winding associated witha well aligned rotor-stator pole pair. I

r 2, Electrical transducer apparatus 'as in claim 1 wherein saidstepping motor has a greater number of stator poles than rotorpoles.

-.3. Electrical transducer apparatus as in claim 1 wherein said steppingmotor has eight stator poles and ate in one semicircular half of saidstator member magcapable of transmitting significant quantities ofmagnetic flux from rotor poles located on one sidethereof to rotor poleslocated on the other side thereof and wherein said electricalwindingsare connected to direct a significant portion of the magnetic fluxgenerated thereby across at least part of said rotor member during atleast part of the operating cycle of said apparatus. 7. Transducerapparatus for converting electrical energy into precise increments ofrotational mechanical energy, said apparatus comprising: an electricalstepping motor member having .ple poledstator portion and a multiplepoled rotor portion, the rotor portion being magnetically rotatable intoa plurality of rotor-stator pole aligned first detent positions byexcitation of electrical windings associated with a singular rotor stepposition and magnetically rotatable into a plurality of I rotorstatorpole misaligned second detent positions located generally intermediatesaid first detent positions by concurrent excitation of electricalwindings associated with at least two of said first detent steppositions; a v electrical exciter means selectively connected withconcurrently excitable electrical windings of said stepping motornon-alignable rotor-stator pole pairs and including a source ofelectrical energy and a chopper modulated current regulator responamultisive to the total current flow in both windings of saidconcurrently excitable non-alignablerotorstator pole pairs, forsupplying to said stepping motor bursts of chopped electrical energycapable of moving said rotor 'memberinto successive'rotationalpositions; 5

whereby a dynamic rotor position responsive division ;of said choppermodulated total current flow occurs between said, concurrently" excitedwindings wherein the larger inductance of a closely aligned rotor-statorpole pair produces a smaller winding current flow therein'and thesmaller inductance of anon-aligned rotor-stator pole pair produces alarger winding current flow therein; and i i whereby the tendency ofsaid ste pping motor member topass by one'of saidirotor-stator polemisaligned second detent positions irian overshoot motion is opposed bya decrease of current and magnetic flux in the stator pole ahead of saidsecond detent position an d an increase of current and magnetic flux inthe stator pole behind said second detent position as said rotor memberrotates through said seconddeten't position. r

8. Transducer apparatus as in claim 7wherein said chopper modulatedcurrent regulator in saidelectrical exciter means includes a currentsensing element,.an amplifier element, and a current switching elementconnectedinto a feed-back loop configuration wherein signals from saidcurrent sensing element pass through said amplifier element and controlthe current conducting time in said current switching element andwherein said current switching element is connected between said sourceof electrical energy and said concurrently excitable electrical windingsfor controlling current flow therebetween. I I I 9. Transducer apparatusas in claim7 whereinsaid chopper modulated current regulator includesclock means for periodically initiating pulses of current in saidstepping motor windings at a rate independent of the electrical timeconstant of said windings.

10. Transducer apparatus as in claim 9 wherein said, clock meansincludeselectrical timing means for initiating pulses of current at a frequencyabove the audio frequency range; l

whereby sound energy emitted by said stepping motor is composedprimarily of frequencies above 'the human audible range. I a a '11.Apparatus for differentially exciting two. electrical windings of amultiple-poled stepping motor, said apparatus comprising:

a source of direct current electrical energy; L a current sensingelement capable of developing a current signal representative of theinstantaneous current flow therein; an electrical switching element;said source of direct current electrical energy, said electricalswitching element, said-current sensing element and aparallelcombination of said two electrical windings being connected together inan exciting current series electrical circuit; and pulsed electricaldriver means having an input node connected with said current sensingelement and an output port connected with said electrical switchingelement in closed feedback loop fashion for driving said electricalswitching element in a pulsed current modulating mode wherein the ratioof conducting and non-conducting time is respon- I sive to saidvcurrentsignal and thereby to the average current flowing in'said excitingcurrent series electrical circuit;

whereby current regulating action of said closed feedback loop maintainsa constant total current flow in said twoelectrical windings and saidconstant total current flow can be instantaneously divided between saidtwo electrical windings accordt ing to the degree of engagement betweenstepping motor rotor and stator poles associated with said windingcircuits.

12. Apparatus for differentially exciting as in claim l 1 wherein saidpulsed electrical driver means includes an input node and a source ofbias signals connected tivity in said electrical switching element;

whereby the pulsing rate of said pulsed electrical driver means may bepositively established at a predetermined frequency.

14. Apparatus for differentially exciting as in claim 11 wherein saidpulsed electrical driver means includes operational amplifier circuitmeans connected as a saturating amplifier pulse width modulator fordetermining time duration of the current modulating pulses in saidelectrical switching element.

15. A method for exciting the electrical windings of a salient polestepping motor of the type having stator windings associated with eachstator pole for reducing rotational overshoot of the motor rotor at anattained stepping position, said method comprising the steps of:

placing the rotor of said stepping motor in motion by altering thepatternof excitation of said stator pole 1 citing current after saidrotor has rotated through a position of maximum alignment with saidpreceding pole; decreasing the magnitude of said following pole excitingcurrent after said rotor has rotated through I a position of maximumalignment with said preceding pole. 16. A method for exciting as inclaim 15 including the step of:

augmenting the-magnitude of said following pole exciting current aftersaid rotor has rotatedthrough a; position of maximum alignment with saidfollowing pole in an over-shoot motion; whereby said rotor is urgedbackward toward said following pole.

i v 17. A method for exciting as in claim 15 including the I step of:

' diminishing the magnitude of said following pole exciting current assaid rotor member re-approaches a position of maximum alignment withsaid follow- 1 ing pole during relaxation from an overshoot motion. 18.A method for exciting as in claim'l5 wherein said exciting current is adirect current having superimposed thereon a pulse modulated regulationcomponent and wherein said preceding pole and following pole currentsare derived from said pulse modulated direct current; whereby saidpreceding pole exciting current and said following pole exciting currentare instantaneously responsive to the electrical inductance and themagnetic reluctance properties of both said preceding pole and saidfollowing pole as thealignment of said preceding and following poleswith poles of said rotor member changes during rotor movement;

19. A method for exciting as in claim 18 wherein said preceding pole andsaid following pole exciting currents are currents deriveddifferentially from said pulse modulated direct current;

whereby the magnitude of said following pole exciting current isresponsive to electrical inductance and magnetic reluctance propertychanges in both said preceding pole and said following pole; and wherebythe magnitude of, said preceding pole exciting current is responsive toelectrical inductance and magnetic reluctance property changes in bothsaid preceding pole and said following pole.

1. Electrical transducer apparatus comprising: an electrical steppingmotor of the type having a rotor member which is magneticallypositionable in a plurality of detent positions each located generallyintermediate two adjacent pole aligned detent positions by simultaneousexcitation of two electrical windings, each winding being associatedwith one pole of said adjacent pole-aligned detent positions; modulatedelectrical exciting means connected differentially with said twoelectrical windings for supplying to said windings differentiallydivided exciting currents having at least an undulating variationimposed thereon; and commutating means connected with each electricalwinding of said stepping motor and with said electrical exciting meansfor diverting said differentially divided exciting current to subsequentpairs of electrical windings; whereby the electrical inductance of eachwinding of said two differentially connected windings is dependent uponthe degree of alignment between rotor and stator poles instantaneouslyassociated with said winding and current division between saiddifferentially connected windings is responsive to said electricalinductance and to said degree of alignment for producing high currentflow in a winding associated with a poorly aligned rotor-stator polepair and low current flow in a winding associated with a well alignedrotor-stator pole pair.
 2. Electrical transducer apparatus as in claim 1wherein said stepping motor has a greater number of stator poles thanrotor poles.
 3. Electrical transducer apparatus as in claim 1 whereinsaid stepping motor has eight stator poles and six rotor poles. 4.Electrical transducer apparatus as in claim 1 wherein said electricalwindings and said commutating means are connected to generate magneticpoles of alternating magnetic polarity around the periphery of saidsTator member.
 5. Electrical transducer apparatus as in claim 1 whereinsaid electrical windings are polarized to generate in one semicircularhalf of said stator member magnetic poles of one polarity and in theremaining semicircular half of said stator member magnetic poles of theopposite polarity.
 6. Electrical transducer apparatus as in claim 1wherein said stepping motor includes a rotor member having materialcomposition and cross sectional shape capable of transmittingsignificant quantities of magnetic flux from rotor poles located on oneside thereof to rotor poles located on the other side thereof andwherein said electrical windings are connected to direct a significantportion of the magnetic flux generated thereby across at least part ofsaid rotor member during at least part of the operating cycle of saidapparatus.
 7. Transducer apparatus for converting electrical energy intoprecise increments of rotational mechanical energy, said apparatuscomprising: an electrical stepping motor member having a multiple poledstator portion and a multiple poled rotor portion, the rotor portionbeing magnetically rotatable into a plurality of rotor-stator polealigned first detent positions by excitation of electrical windingsassociated with a singular rotor step position and magneticallyrotatable into a plurality of rotor-stator pole misaligned second detentpositions located generally intermediate said first detent positions byconcurrent excitation of electrical windings associated with at leasttwo of said first detent step positions; electrical exciter meansselectively connected with concurrently excitable electrical windings ofsaid stepping motor non-alignable rotor-stator pole pairs and includinga source of electrical energy and a chopper modulated current regulatorresponsive to the total current flow in both windings of saidconcurrently excitable non-alignable rotor-stator pole pairs, forsupplying to said stepping motor bursts of chopped electrical energycapable of moving said rotor member into successive rotationalpositions; whereby a dynamic rotor position responsive division of saidchopper modulated total current flow occurs between said concurrentlyexcited windings wherein the larger inductance of a closely alignedrotor-stator pole pair produces a smaller winding current flow thereinand the smaller inductance of a non-aligned rotor-stator pole pairproduces a larger winding current flow therein; and whereby the tendencyof said stepping motor rotor member to pass by one of said rotor-statorpole misaligned second detent positions in an overshoot motion isopposed by a decrease of current and magnetic flux in the stator poleahead of said second detent position and an increase of current andmagnetic flux in the stator pole behind said second detent position assaid rotor member rotates through said second detent position. 8.Transducer apparatus as in claim 7 wherein said chopper modulatedcurrent regulator in said electrical exciter means includes a currentsensing element, an amplifier element and a current switching elementconnected into a feed-back loop configuration wherein signals from saidcurrent sensing element pass through said amplifier element and controlthe current conducting time in said current switching element andwherein said current switching element is connected between said sourceof electrical energy and said concurrently excitable electrical windingsfor controlling current flow therebetween.
 9. Transducer apparatus as inclaim 7 wherein said chopper modulated current regulator includes clockmeans for periodically initiating pulses of current in said steppingmotor windings at a rate independent of the electrical time constant ofsaid windings.
 10. Transducer apparatus as in claim 9 wherein said clockmeans includes electrical timing means for initiating pulses of currentat a frequency above the audio frequency range; whereby sound energyemitted by said stepping motor is composed primarily of frequenciesabove the human audible range.
 11. Apparatus for differentially excitingtwo electrical windings of a multiple-poled stepping motor, saidapparatus comprising: a source of direct current electrical energy; acurrent sensing element capable of developing a current signalrepresentative of the instantaneous current flow therein; an electricalswitching element; said source of direct current electrical energy, saidelectrical switching element, said current sensing element and aparallel combination of said two electrical windings being connectedtogether in an exciting current series electrical circuit; and pulsedelectrical driver means having an input node connected with said currentsensing element and an output port connected with said electricalswitching element in closed feedback loop fashion for driving saidelectrical switching element in a pulsed current modulating mode whereinthe ratio of conducting and non-conducting time is responsive to saidcurrent signal and thereby to the average current flowing in saidexciting current series electrical circuit; whereby current regulatingaction of said closed feedback loop maintains a constant total currentflow in said two electrical windings and said constant total currentflow can be instantaneously divided between said two electrical windingsaccording to the degree of engagement between stepping motor rotor andstator poles associated with said winding circuits.
 12. Apparatus fordifferentially exciting as in claim 11 wherein said pulsed electricaldriver means includes an input node and a source of bias signalsconnected thereto for altering the ratio of conducting andnon-conducting times in said electrical switching element; whereby biassignals for altering the magnitude of current flowing in said excitingcurrent series electrical circuit may be applied to said apparatus. 13.Apparatus for differentially exciting as in claim 11 wherein said pulsedelectrical driver means includes clock timing means for periodicallyinitiating conductivity in said electrical switching element; wherebythe pulsing rate of said pulsed electrical driver means may bepositively established at a predetermined frequency.
 14. Apparatus fordifferentially exciting as in claim 11 wherein said pulsed electricaldriver means includes operational amplifier circuit means connected as asaturating amplifier pulse width modulator for determining time durationof the current modulating pulses in said electrical switching element.15. A method for exciting the electrical windings of a salient polestepping motor of the type having stator windings associated with eachstator pole for reducing rotational overshoot of the motor rotor at anattained stepping position, said method comprising the steps of: placingthe rotor of said stepping motor in motion by altering the pattern ofexcitation of said stator pole windings; energizing the stator polesimmediately preceding and immediately following the next intended reststepping position of said rotor with a preceding pole and a followingpole exciting current, said next intended rest stepping position beinglocated generally midway between said immediately preceding and saidimmediately following stator poles; increasing the magnitude of saidpreceding pole exciting current after said rotor has rotated through aposition of maximum alignment with said preceding pole; decreasing themagnitude of said following pole exciting current after said rotor hasrotated through a position of maximum alignment with said precedingpole.
 16. A method for exciting as in claim 15 including the step of:augmenting the magnitude of said following pole exciting current aftersaid rotor has rotated through a position of maximum alignment with saidfollowing pole in an over-shoot motion; whereby said rotor is urgedbackward toward said following pole.
 17. A method for exciting as inclaim 15 including the steP of: diminishing the magnitude of saidfollowing pole exciting current as said rotor member re-approaches aposition of maximum alignment with said following pole during relaxationfrom an overshoot motion.
 18. A method for exciting as in claim 15wherein said exciting current is a direct current having superimposedthereon a pulse modulated regulation component and wherein saidpreceding pole and following pole currents are derived from said pulsemodulated direct current; whereby said preceding pole exciting currentand said following pole exciting current are instantaneously responsiveto the electrical inductance and the magnetic reluctance properties ofboth said preceding pole and said following pole as the alignment ofsaid preceding and following poles with poles of said rotor memberchanges during rotor movement.
 19. A method for exciting as in claim 18wherein said preceding pole and said following pole exciting currentsare currents derived differentially from said pulse modulated directcurrent; whereby the magnitude of said following pole exciting currentis responsive to electrical inductance and magnetic reluctance propertychanges in both said preceding pole and said following pole; and wherebythe magnitude of said preceding pole exciting current is responsive toelectrical inductance and magnetic reluctance property changes in bothsaid preceding pole and said following pole.